1. Field of the Invention
This invention relates to a high-pressure generating device for generating high-pressure fluid like a high-pressure pump for ejecting a water jet, a gas compressor for discharging gas such as air and a compressor for discharging various fluids at high pressure.
2. Description of the Related Art
There has been used a plunger pump (sometimes called “piston pump”) for discharging fluid, especially, aqueous fluid at high pressure. The plunger pump can eject the fluid by introducing the fluid into a cylinder and driving a piston in the cylinder with kinetic energy given from an external power source to energize the fluid within the cylinder. Further, there are plenty of other pumps capable of ejecting fluid such as an axial type pump, an in-line piston pump, a vane pump, and a gear pump. Since any pump of this type inevitably carries out compression motion, it necessitates a plurality of pistons to stably generate a required discharge pressure with small pulsation of flow.
Japanese Examined Patent Publication SHO 62-21994(B) discloses a pressure transforming device comprising two pairs of pistons and cylinders for discharging high-pressure hydraulic oil by automatically reciprocating the pistons.
Of gas compressors as seen in an air conditioner, there are various types of pumps such as of a plunger type and a vane type. Most of pumps of these types have functions of compressing gas such as air introduced thereinside by reciprocating the pistons or an equivalent thereof and equalizing the pressure of the compressed air or gas discharged therefrom.
In compressing the gas, a multistage type pump can efficiently compress the gas at high pressure in comparison with a single-stage type pump. As shown in FIG. 23 by way of example, there has been known a multistage gas compressor 99 having piston means C1, C2 and C3 serially connected with one another and driven eccentrically by an electric motor M through an eccentric driving shaft. Each piston means of the conventional compressor 99 includes a cylinder having an inner diameter gradually decreased from the intake side toward the outlet side thereof so as to readily compress the gas G.
Of the aforementioned plunger pump for compressing liquid, a non-pulsation type pump capable of uniformly producing liquid pressure with no pulsation of pressure is preferably used. The fluctuation of the discharge pressure can be lessened with increasing the number of pistons, but the increase of the pistons disadvantageously results in increasing the overall size of the pump and the production costs. Moreover, even the plunger pump having a relatively large number of pistons frequently causes pulsating flow Δp with large discharge pressure p, as illustrated in FIG. 21 by way of example.
Where compressing liquid from a non-pressurized state (zero pressure state), it will wastefully take time to increase the pressure to a prescribed pressure level, since the liquid to be compressed contains air in most cases. Such a waste of time is negligible. For instance, pressure drop in cutting a material at high speed with a water jet may possibly cause imperfect cutting. In a case of precisely controlling the depth of cut to be formed in the surface of the material, it is desirable to use a non-pulsation type pump or a similar high pressure pump capable of constantly producing a prescribed pressure, but there has been no such pump capable of fulfilling the desired function.
In the conventional pressure transforming device described in Japanese Examined Patent Publication SHO 62-21994(B), it has also commenced to compress the fluid from the zero pressure state in the compression stroke of one piston. However, the pump of the conventional device entails a disadvantage such that the discharge pressure p thus produced undergoes a pulsating change as shown in FIG. 22(a). Consequently, this conventional pump cannot be suitably used for a water jet and so on.
Although increasing of the number of pistons may diminish the pulsation in pressure of the fluid discharged from the gas compressor similarly to the plunger pump, it brings about an inconvenience of increasing the size of the pump and driving up the cost of production. Furthermore, the aforenoted multistage gas compressor 99 having the multiple cylinders with pistons, which are connected with one another through pipes becomes complicated and expensive and is not applicable to a pressure system, which has been recently forced to take prompt measures against an environmental chlorofluorocarbon problem.